EMI stands for electromagnetic interference, the disruption that happens when energy from one electronic device interferes with the normal operation of another. Every electronic device produces some level of electromagnetic energy, whether intentionally (like a cell phone transmitting a signal) or as a byproduct of its operation (like a motor or power supply). When that energy reaches a nearby device and causes it to malfunction, produce errors, or degrade in performance, that’s EMI.
How EMI Works
EMI follows a simple three-part model: a source, a path, and a receptor. The source generates electromagnetic energy. The path carries that energy to another device. The receptor picks it up and reacts to it. If any one of those three elements is missing, interference doesn’t occur.
The path between source and receptor takes one of two forms. Radiated interference travels through the air as electromagnetic waves, the same way a radio station’s signal reaches your car. Conducted interference travels along physical connections like power cables, USB cords, or other wiring shared between devices. In many real-world situations, both types happen at once.
Common Sources of EMI
Some devices generate EMI on purpose because they need electromagnetic waves to function. Cell phones, Wi-Fi routers, Bluetooth speakers, and radio transmitters all fall into this category. They’re designed to emit energy at specific frequencies, but that energy can still interfere with nearby electronics that weren’t designed to handle it.
Other devices produce EMI as an unintended side effect. Electric motors, welding machines, treadmills, power inverters, and even basic household appliances all generate electromagnetic noise during normal operation. Microwave ovens are a classic example. They operate at 2.4 GHz, the same frequency band used by many Wi-Fi routers, which is why your internet connection can stutter when you heat up leftovers.
Why EMI Matters in Everyday Life
For most consumer electronics, EMI shows up as minor annoyances: a buzzing sound through speakers, a flickering monitor, or a momentary glitch in a wireless connection. These problems are usually harmless. But in settings where electronics control critical systems, the stakes are much higher.
Medical devices are particularly sensitive. Implanted pacemakers and defibrillators can be affected by strong electromagnetic fields. In hospital settings, research has shown that surgical tools using electrical current can cause interference with implanted heart devices when used within about 8 cm (roughly 3 inches) of the device. This is why surgical teams take specific precautions to keep electromagnetic sources as far from implants as possible during procedures.
MRI machines present another example. The powerful magnetic and radiofrequency fields inside an MRI scanner induce electrical currents in any metallic object in the machine’s bore. For patients with metal implants, those induced currents can heat the surrounding tissue to dangerous levels. The effect is most pronounced when the length of a metallic implant happens to match a fraction of the radiofrequency wavelength, creating what engineers call an “antenna effect” that concentrates energy at the implant’s tips.
EMI and 5G Networks
As 5G wireless networks have expanded, questions about whether new frequencies pose additional risks to people with implanted heart devices have come up frequently. A study testing 384 scenarios across pacemakers and implantable defibrillators found that none of the tested devices showed interference at 3.6 GHz, one of the primary 5G bands. Researchers did observe 43 interference events at 700 MHz (a lower 5G frequency), but these occurred at power levels and distances that don’t reflect normal phone use. The standard safety recommendation of keeping your phone at least 15 cm (about 6 inches) from an implanted heart device still holds for 5G.
How EMI Is Controlled
Reducing EMI comes down to three strategies: block the energy at the source, interrupt the path, or harden the receptor so it’s less susceptible.
- Shielding is the most common approach. Metal enclosures around sensitive electronics reflect and absorb incoming electromagnetic waves before they reach internal circuits. Aluminum foil, for instance, is effective primarily through absorption despite being extremely thin. The weak points in any shield are the seams and joints, which is why manufacturers use conductive gaskets (springy, electrically conductive strips) to seal gaps in enclosures.
- Filtering targets conducted interference. Filters on power lines and signal cables block unwanted electromagnetic noise from traveling between devices through shared wiring.
- Grounding gives stray electrical energy a safe path to dissipate rather than building up and radiating outward.
Regulations That Limit EMI
Governments regulate how much electromagnetic energy devices are allowed to emit. In the United States, the FCC’s Part 15 rules set emission limits for digital devices and unintentional radiators, meaning any electronic product that generates electromagnetic energy as a byproduct. Every consumer electronic device sold in the U.S. must comply with these limits, which is why you’ll find FCC compliance labels on computers, routers, and televisions.
Medical devices face their own, often stricter, requirements. The FDA recognizes the IEC 60601-1-2 standard for non-implantable medical equipment, which sets both emission limits (how much EMI a device can produce) and immunity levels (how much EMI it must tolerate without malfunctioning). Implantable devices like pacemakers follow separate standards under the ISO 14117 and ISO 14708 series. These standards define the minimum power levels at which an implant must continue functioning normally, even in the presence of electromagnetic fields.
EMI in Hospitals
Hospitals are uniquely challenging environments for EMI because they concentrate large numbers of sensitive electronic devices in close proximity to powerful electromagnetic sources. MRI machines, electrosurgical tools, patient monitors, wireless communication systems, and building infrastructure all coexist in a relatively small space.
The FDA recommends that healthcare facilities assign responsibility for electromagnetic compatibility to their clinical engineering teams, assess the electromagnetic environment of critical care areas like emergency rooms and intensive care units, and establish written policies for managing interference risks. Staff, visitors, and patients should all be educated about EMI, including how to recognize it. Hospitals are also encouraged to consider electromagnetic compatibility during facility design, not just after problems arise, by coordinating the purchase and placement of all electronic equipment to minimize conflicts between devices.